Programmed Death-ligand 1 Expression Research Articles

Circ_0027791 contributes to the growth and immune evasion of hepatocellular carcinoma via the miR-496/programmed cell death ligand 1 axis in an m6A-dependent manner.

Emerging evidence indicates the critical roles of circular RNAs in the development of multiple cancers, containing hepatocellular carcinoma (HCC). Herein, our present research reported the biological function and mechanism of circ_0027791 in HCC progression. Circ_0027791, microRNA-496 (miR-496), programmed cell death ligand 1 (PDL1), and methyltransferase-like 3 (METTL3) levels were detected by real-time quantitative polymerase chain reaction (RT-qPCR). Cell viability, proliferation, invasion, and sphere formation ability were detected using 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide, 5-ethynyl-2'-deoxyuridine, transwell, and sphere formation assays. Macrophage polarization was detected using flow cytometry assay. To understand the role of circ_0027791 during the immune escape, HCC cells were cocultured with peripheral blood mononuclear cells or cytokine-induced killer (CIK) cells in vitro. A xenograft mouse model was applied to assess the function of circ_0027791 in vivo. After prediction using circinteractome and miRDB, the binding between miR-496 and circ_0027791 or PDL1 was validated based on a dual-luciferase reporter assay. Interaction between METTL3 and circ_0027791 was determined using methylated RNA immunoprecipitation (MeRIP)-qPCR, RIP-qPCR, and RNA pull-down assays. Circ_0027791, PDL1, and METTL3 expression were upregulated, and miR-496 was decreased in HCC patients and cells. Moreover, circ_0027791 knockdown might repress proliferation, invasion, sphere formation, M2 macrophage polarization, and antitumor immune response. Circ_0027791 knockdown repressed HCC tumor growth in vivo. In mechanism, circ_0027791 functioned as a sponge for miR-496 to increase PDL1 expression. In addition, METTL3 mediated the m6A methylation of circ_0027791 and stabilized its expression. METTL3-induced circ_0027791 facilitated HCC cell progression partly regulating the miR-496/PDL1 axis, which provided a new prognostic and therapeutic marker for HCC.

A real-world retrospective, observational study of first-line pembrolizumab plus chemotherapy for metastatic non-squamous non-small cell lung cancer with PD-L1 tumor proportion score < 50% (PEMBROREAL).

The phase III Keynote-189 trial established a first-line treatment combining pembrolizumab with pemetrexed and platinum as a standard treatment for patients with stage IV non-small cell lung cancer (NSCLC) without known EGFR and ALK driver mutations and independent of programmed cell death ligand 1 (PD-L1) expression. However, in Italy, eligibility for the National Health Service payment program is limited to patients with PD-L1 <50%. The PEMBROREAL study assesses the real-world effectiveness and safety of pembrolizumab in patients eligible for the National Health Service payment program. PEMBROREAL is a retrospective, observational study on patients with NSCLC who started pembrolizumab combined with pemetrexed and platinum within the reimbursability time window, considered as December 2019 to December 2020. The primary endpoints were to assess progression-free survival (PFS) and overall survival (OS; using the Kaplan-Meier method), response to therapy, and tolerability. Until February 2022, 279 patients (median follow-up: 19.7 months) have been observed. The median PFS was 8.0 months (95% confidence interval: 6.5-9.2). OS was not reached, but we can estimate a 12- to 24-month survival rate for the combined treatment: 66.1% and 52.5%, respectively. PD-L1 expression and Eastern Cooperative Group (ECOG) Performance Status were both associated with PFS and OS. Overall, only 44.4% of patients reported an adverse event, whereas toxicity led to a 5.4% discontinuation rate. The results of the PEMBROREAL study have shown that the combined treatment of pembrolizumab with pemetrexed and platinum is effective for metastatic non-squamous NSCLC, even for patients with PD-L1 levels below 50%, despite the differences in patient demographics and pathological features compared to the Keynote-189 study. The adverse events reported during the study were more typical of chemotherapy treatment rather than immunotherapy, and physicians were able to manage them easily.

Metabolic Tumor Volume as Significant Predictor for Chemotherapy Containing PD-L1 Blocker in Extensive Stage Small Cell Lung Cancer.

Chemo-immunotherapy, including the programmed death ligand 1 (PD-L1) antibody, is an effective treatment for patients with extensive-stage small-cell lung cancer (ES-SCLC). However, no biomarker has been established for the prediction of chemo-immunotherapy. Therefore, we investigated the potential of 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) as a predictive marker. Forty-six patients with ES-SCLC who received 18F-FDG-PET immediately before combined platinum-based chemotherapy with PD-L1 blockade as a first-line treatment were eligible, and the maximum standard uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) on 18F-FDG uptake were evaluated. PD-L1 and tumor infiltrative lymphocytes (TILs) were immunohistochemically analyzed in 36 of the 46 patients. A high MTV was significantly associated with poor performance status and low albumin levels, and there was a significant association between low albumin and high TLG. Univariate analysis identified sex, Brinkman index, and MTV as significant predictors of progression-free survival (PFS), and sex, SUVmax, MTV, and TLG as significant factors of overall survival (OS). Multivariate analysis revealed that sex, Brinkman index, and MTV were independent prognostic factors for PFS, and sex, SUVmax, MTV, and TLG were significant predictors of OS. SUVmax was significantly higher in patients with positive PD-L1 expression than in those with negative expression but was not significantly different between positive and negative TILs. Moreover, the levels of MTV and TLG were not closely associated with the levels of PD-L1 and TILs. MTV or TLG metabolic tumor activity is suitable for the prediction of chemo-immunotherapy outcomes in patients with ES-SCLC.

Metformin Suppresses Both PD-L1 Expression in Cancer Cells and Cancer-Induced PD-1 Expression in Immune Cells to Promote Antitumor Immunity.

Metformin, a drug prescribed for patients with type 2 diabetes, has potential efficacy in enhancing antitumor immunity; however, the detailed underlying mechanisms remain to be elucidated. Therefore, we aimed to identify the inhibitory molecular mechanisms of metformin on programmed death ligand 1 (PD-L1) expression in cancer cells and programmed death 1 (PD-1) expression in immune cells. We employed a luciferase reporter assay, quantitative real-time PCR, immunoblotting analysis, immunoprecipitation and ubiquitylation assays, and a natural killer (NK) cell-mediated tumor cell cytotoxicity assay. A mouse xenograft tumor model was used to evaluate the effect of metformin on tumor growth, followed by flow-cytometric analysis using tumor-derived single-cell suspensions. Metformin decreased AKT-mediated β-catenin S552 phosphorylation and subsequent β-catenin transactivation in an adenosine monophosphate-activated protein kinase (AMPK) activation-dependent manner, resulting in reduced CD274 (encoding PD-L1) transcription in cancer cells. Tumor-derived soluble factors enhanced PD-1 protein stability in NK and T cells via dissociation of PD-1 from ubiquitin E3 ligases and reducing PD-1 polyubiquitylation. Metformin inhibited the tumor-derived soluble factor-reduced binding of PD-1 to E3 ligases and PD-1 polyubiquitylation, resulting in PD-1 protein downregulation in an AMPK activation-dependent manner. These inhibitory effects of metformin on both PD-L1 and PD-1 expression ameliorated cancer-reduced cytotoxic activity of immune cells in vitro and decreased tumor immune evasion and growth in vivo. Metformin blocks both PD-L1 and PD-1 within the tumor microenvironment. This study provided a mechanistic insight into the efficacy of metformin in improving immunotherapy in human cancer.

PD-L1 Expression in Colorectal Carcinoma Correlates with the Immune Microenvironment.

Colorectal carcinoma (CRC) is a common malignancy, with its diverse clinical, pathological, and molecular features. The immune microenvironment of a tumor comprises of interplay between various cells and molecules, and has a significant role in deciding the tumor behavior and overall prognosis. PD-L1 (programmed cell death ligand-1) has been implicated in the regulation of the tumor immune microenvironment (TIME). There is limited data regarding the correlation of PD-L1 expression with immune cell profile in CRCs, especially in the Indian setting. The study aimed to assess the PD-L1 expression in CRC tumor cells and its association with TIME, mismatch repair (MMR), and various other clinicopathological parameters. This is a hospital-based, cross-sectional observational study. PD-L1 expression was assessed at the protein level by immunohistochemistry and mRNA level by qRT-PCR. Immune cell markers (CD4, CD8, CD20, FOXP3, and CD163) were interpreted using the ImageJ Fiji platform. Of the 104 cases, 21% were PD-L1 positive and were more common in right-sided CRCs. PD-L1 positive cases showed significantly higher concentrations of all T-cell subsets (CD4+ , CD8+ , and FOXP3+), CD20+ B-cells, and CD163+ macrophages were noted. No statistical significance was seen between PD-L1 expression with clinical profile, pathological subtype, grade or stage, mismatch repair status (proficient vs deficient), and survival. The present study showed a relatively lower frequency of PD-L1 in CRC from the Eastern Indian cohort. The immune cell concentration in the present study was calculated using image analysis-based objectivised methods. Significant correlation of PD-L1 expression in tumor cells with the tumor-infiltrating immune cells indicated its crucial role in the pathobiology of CRC especially by regulating the TIME. Considering the therapeutic implication of PD-L1 in various malignancies, it may be one of the crucial therapeutic targets in a proportion of cases.

Comparing deep learning and pathologist quantification of cell-level PD-L1 expression in non-small cell lung cancer whole-slide images

Programmed death-ligand 1 (PD-L1) expression is currently used in the clinic to assess eligibility for immune-checkpoint inhibitors via the tumor proportion score (TPS), but its efficacy is limited by high interobserver variability. Multiple papers have presented systems for the automatic quantification of TPS, but none report on the task of determining cell-level PD-L1 expression and often reserve their evaluation to a single PD-L1 monoclonal antibody or clinical center. In this paper, we report on a deep learning algorithm for detecting PD-L1 negative and positive tumor cells at a cellular level and evaluate it on a cell-level reference standard established by six readers on a multi-centric, multi PD-L1 assay dataset. This reference standard also provides for the first time a benchmark for computer vision algorithms. In addition, in line with other papers, we also evaluate our algorithm at slide-level by measuring the agreement between the algorithm and six pathologists on TPS quantification. We find a moderately low interobserver agreement at cell-level level (mean reader-reader F1 score = 0.68) which our algorithm sits slightly under (mean reader-AI F1 score = 0.55), especially for cases from the clinical center not included in the training set. Despite this, we find good AI-pathologist agreement on quantifying TPS compared to the interobserver agreement (mean reader-reader Cohen’s kappa = 0.54, 95% CI 0.26–0.81, mean reader-AI kappa = 0.49, 95% CI 0.27—0.72). In conclusion, our deep learning algorithm demonstrates promise in detecting PD-L1 expression at a cellular level and exhibits favorable agreement with pathologists in quantifying the tumor proportion score (TPS). We publicly release our models for use via the Grand-Challenge platform.

Abstract 5099: Prevalence of fibroblast growth factor receptor (FGFR) alterations (alts) and programmed death-ligand 1 (PD-L1) expression (exp) in Chinese solid tumor patients (pts)

Abstract Background: PD-L1 expression drives anti-PD(L)-1 treatment decisions across many cancer indications. FGFR inhibitors have been approved for the treatment of metastatic urothelial cancer (UC) and cholangiocarcinoma with FGFR alts. BALVERSA (erdafitinib), a selective pan-FGFR kinase inhibitor, has shown clinical activity against FGFR altered solid tumors in pts who exhausted standard treatment options. It is important to understand the prevalence of FGFR alts and relationship between FGFR alts and PD-L1 expression levels in different cancer types. Methods: In this real-world study, 9937 Chinese solid tumor pts with the PD-L1 (22C3) immunohistochemistry and OrigiMed 450-gene next-generation sequencing panel results were selected. Chi-square test and Fisher test were used to explore the association between the FGFR alts and PD-L1 expression. Results: FGFR1-4 somatic alts were found in 9.0% of Chinese cancer pts evaluated. FGFR1 amplification (amp) was the most prevalent alts identified (1.9%). There were no significant differences in frequency of FGFR alts between the Chinese cohort and MSK-IMPACT cohort in each cancer type tested. Up to 40.6% of pts evaluated were PD-L1 positive (CPS ≥1 or TPS ≥1%). The PD-L1 positive rate (TPS ≥1%) in SCLC (12.4%, n=121) and NSCLC adenocarcinoma tumors (LUAD) (26.1%, n=2902) was relatively low. In few tumor types, higher expression of PD-L1 in FGFR altered samples was observed compared with FGFR unaltered samples in pan-tumor (mean TPS 14.8% vs.8.6%, P=6.0*E-9; mean CPS 6.3 vs. 6.1, P=3*E-4). Those includes LUAD (mean TPS 14.2% vs. 7.4%, P = 1.7*E-16), colorectal tumor (mean CPS 4.6 vs. 3.9, P = 4.6*E-8), and uterine tumor (mean CPS 8.1 vs. 6.5, P = 9.6*E-5). While PD-L1 expression is lower in FGFR altered samples than FGFR unaltered samples in UC (n=154; mean CPS 3.9 vs. 6.8, P = 0.004). No relationship was observed between FGFR alts and PD-L1 expression in cholangiocarcinoma (n=610). Specific FGFR alts eligible for erdafitinib UC treatment were further investigated in UC and observed with rate 10.4%, including FGFR3 short variants (9.7%) as main alts. Specific FGFR altered tumors showed similar trend with lower PD-L1 expression than FGFR unaltered tumors in UC. The inverse relationship between FGFR alts and PD-L1 expression in UC compared to other solid tumors may explain variable role of FGFRs since the predominant FGFR alt types vary among different cancer types (FGFR3 short variants enriched in UC vs no such predominant FGFR alt types in other cancer types). Conclusion: The large Chinese solid tumor cohort analysis showed comparable FGFR alts prevalence between Chinese and Western population. Differences in relationship between FGFR alts and PD-L1 expression across tumor types reflect the differential role of predominant FGFR types in each tumor type. Citation Format: Min Qing, Fei Yang, Xiaowei Chen, Xuesong Lyu, Aodi Wang, Yanfei Yu, Shibu Thomas, Longen Zhou. Prevalence of fibroblast growth factor receptor (FGFR) alterations (alts) and programmed death-ligand 1 (PD-L1) expression (exp) in Chinese solid tumor patients (pts) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5099.

Abstract 5146: Clinical significance of inter-assay discrepancy in PD-L1 expression evaluation for the efficacy of pembrolizumab in advanced NSCLC patients with high PD-L1 expression

Abstract Introduction: The expression of programmed cell death ligand-1 (PD-L1) is a predictive biomarker for the efficacy of pembrolizumab in advanced non-small cell lung cancer (NSCLC). While several assays have been approved for evaluating PD-L1 expression status, the inter-assay discordances are observed. The clinical significance of these discrepancies is still unclear. Methods: We retrospectively reviewed treatment-naïve NSCLC patients with available PD-L1 expression status by both 22C3 and SP142 assays. Among these patients, efficacy analysis was performed in those with PD-L1 tumor proportion score (TPS) ≥ 50% (22C3) who received the first-line pembrolizumab monotherapy. Additionally, we conducted RNA-sequence analysis in the patients with TPS ≥ 50% to investigate the distinct immune profiles with the inter-assay discordance. Results: A total of 611 patients were evaluated for PD-L1 expression status by both assays. Of 198 patients with TPS ≥ 50%, 91 (46%) had TC score ≤ 1 (SP142, i.e., inter-assay discrepancy). In 52 patients who received the first-line pembrolizumab monotherapy, the efficacy in patients with the inter-assay discrepancy was significantly lower than those without the discrepancy (shown in Table). While there was no difference in tumor microenvironments such as the tumor-infiltrating lymphocytes, the transcriptome analysis revealed significantly more CD274 splicing variants with aberrant 3’-terminal sequences in tumors with the inter-assay discrepancy than those without discrepancy, leading to the suppressed PD-1/PD-L1 pathway in those with the discrepancy. Conclusion: The inter-assay discrepancy in the PD-L1 expression status on tumor cells between the 22C3 and SP142 assays, reflecting an imbalance of the CD274 splicing variants, could be a primary-resistance mechanism to the pembrolizumab monotherapy in highly PD-L1-expressing NSCLCs. PD-L1(22C3) Discrepancy Pts. ORR(%) p value Median PFS(months) 95%CI p value TPS ≥ 50% yes 17 18 &amp;lt; 0.001 3.2 0.8–5.5 &amp;lt; 0.001 no 35 83 8.3 5.7–24.2 Citation Format: Jun Miyakoshi, Jumpei Kashima, Masayuki Shirasawa, Masahiro Torasawa, Yuji Matsumoto, Ken Masuda, Yuki Shinno, Yusuke Okuma, Tatsuya Yoshida, Yasushi Goto, Hidehito Horinouchi, Kouya Shiraishi, Takashi Kohno, Noboru Yamamoto, Yasushi Yatabe, Yuichiro Ohe. Clinical significance of inter-assay discrepancy in PD-L1 expression evaluation for the efficacy of pembrolizumab in advanced NSCLC patients with high PD-L1 expression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5146.

Abstract 3987: PD-L1 antigen stability using PD-L1 IHC pharmDx on human cancer tissues

Abstract Diagnostic evaluation and selection of potential pembrolizumab-responsive patients is achieved by determining the programmed cell death ligand-1 (PD-L1) expression using the companion diagnostic PD-L1 IHC 22C3 pharmDx assay, for several indications. PD-L1 expression is evaluated by immunohistochemistry (IHC) and is currently the most widely used selective biomarker for response to pembrolizumab anti-PD-1 therapy. Antigen stability on cut tissue sections, also referred to as cut section stability (CSS), and its impact on IHC results is of interest when determining PD-L1 positive or negative status for clinical trials and diagnostic purposes. Since the stability of cut sections from formalin-fixed paraffin-embedded (FFPE) tissue relies on retention of PD-L1 antigenicity following tissue sectioning, the aim of these studies was to measure CSS across multiple tumor indications using combined positive score (CPS). The impact of aged cut sections was evaluated for PD-L1 expression based on pathologist CPS scores of blinded and randomized stained sections. To assess CSS, fresh unstained 4µm cut tissue sections were stored in the dark at 2-8 °C. Staining was performed according to the instructions for use at predefined timepoints. Studies included neoplastic specimens from biliary tract adenocarcinoma (BTAC), cervical cancer (CC), colorectal (CRC) and gastric (GC) carcinoma, esophageal cancer (EC), head and neck squamous cell carcinoma (HNSCC), nasopharyngeal (NPC), ovarian (OC), renal cell (RCC), and triple negative breast (TNBC) carcinoma. Data for each indication and timepoint were used to evaluate average drift in CPS scores over time, starting with scores from a set of respective slides stained at timepoint zero, prior to aging of unstained cut slides. CSS for each specimen within each indication was based on the intersection point of the two-sided 95% confidence interval for the regression line on CPS drift with allowable drift limits. Overall CSS for each indication was defined based on the specimen that exhibited the shortest shelf-life. Linear regression analysis was performed to evaluate average CPS drift over time and define the CSS per indication. This analysis identified the following CSS (in days) for each tumor type when stored at 2-8 °C: 105 (CC), 113 (OC), 115 (BTAC), 135 (EC), 163 (GC), 180 (RCC), 197 (HNSCC), 231 (TNBC), 240 (NPC), and 300 (CRC). The minimal shelf life for unstained cut sections stored at 2-8 °C across the 10 indications in these studies was 105 days, indicating a possible minimum threshold for indications tested when sectioned specimens are stored at 2-8 °C. These data provide high confidence in determining PD-L1 expression on properly stored aged cut sections. Commercial claims may be shorter based on region, as specified in the local instructions for use. Citation Format: Megan Kalpakoff, Emily Olander, Kelci Jones, Stephanie Hund, Tiffany Evans, Joseph Barreto, Deanna Moquin, Grant Toland, Siena Tabuena-Frolli, Kristopher Kersch, Karina Kulangara, Jeanette Musser. PD-L1 antigen stability using PD-L1 IHC pharmDx on human cancer tissues [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3987.

CDKL1 potentiates the antitumor efficacy of radioimmunotherapy by binding to transcription factor YBX1 and blocking PD-L1 expression in lung cancer

BackgroundThe evasion of the immune response by tumor cells through programmed death-ligand 1 (PD-L1) has been identified as a factor contributing to resistance to radioimmunotherapy in lung cancer patients. However, the precise molecular mechanisms underlying the regulation of PD-L1 remain incompletely understood. This study aimed to investigate the role of cyclin-dependent kinase-like 1 (CDKL1) in the modulation of PD-L1 expression and the response to radioimmunotherapy in lung cancer.MethodsThe tumorigenic roles of CDKL1 were assessed via cell growth, colony formation, and EdU assays and an in vivo nude mouse xenograft model. The in vitro radiosensitization effect of CDKL1 was evaluated using a neutral comet assay, γH2AX foci formation analysis, and a clonogenic cell survival assay. The protein‒protein interactions were confirmed via coimmunoprecipitation and GST pulldown assays. The regulation of PD-L1 by CDKL1 was evaluated via chromatin immunoprecipitation (ChIP), real-time quantitative PCR, and flow cytometry analysis. An in vitro conditioned culture model and an in vivo C57BL/6J mouse xenograft model were developed to detect the activation markers of CD8+ T cells and evaluate the efficacy of CDKL1 overexpression combined with radiotherapy (RT) and an anti-PD-L1 antibody in treating lung cancer.ResultsCDKL1 was downregulated and suppressed the growth and proliferation of lung cancer cells and increased radiosensitivity in vitro and in vivo. Mechanistically, CDKL1 interacted with the transcription factor YBX1 and decreased the binding affinity of YBX1 for the PD-L1 gene promoter, which consequently inhibits the expression of PD-L1, ultimately leading to the activation of CD8+ T cells and the inhibition of immune evasion in lung cancer. Moreover, the combination of CDKL1 overexpression, RT, and anti-PD-L1 antibody therapy exhibited the most potent antitumor efficacy against lung cancer.ConclusionsOur findings demonstrate that CDKL1 plays a crucial role in regulating PD-L1 expression, thereby enhancing the antitumor effects of radioimmunotherapy. These results suggest that CDKL1 may be a promising therapeutic target for the treatment of lung cancer.

Abstract 6445: Exploring the relationship between PSCA and PD-L1 by a comprehensive tumor immunohistochemical analysis

Abstract Prostate Stem Cell Antigen (PSCA) is a well-established diagnostic marker in various cancers and a promising target for immunotherapy. Programmed Death-Ligand 1 (PD-L1) plays a crucial role in cancer immune regulation and is known to influence patient response to checkpoint inhibitors. The objective of this study is to elucidate the relationship between PSCA and PD-L1 in diverse cancer types and to provide valuable insights for the development of an effective immunotherapy strategy. To accomplish this, immunohistochemical (IHC) analysis was conducted on paraffin-embedded Cytosections obtained from 20 lung cancers, 20 prostate cancers, 32 bladder cancers, and 20 normal tissues for each respective cancer type. Antibodies generated by Origene were utilized to detect the expression of PSCA and PD-L1 on the cell surface. The IHC results of tumor tissue were standardized against corresponding normal samples, and the correlation between these two genes was statistically analyzed using analysis of variance (ANOVA). The findings reveal a significant positive correlation between the expression of PSCA and PD-L1 (r=+0.78, P=0.016), suggesting an underlying mechanism driving their co-expression in the studied cancers. Understanding PSCA and PD-L1 coexpression in bladder, lung, and prostate cancers has great potential for informing tailored immunotherapies. Future research should explore functional consequences within the tumor microenvironment, advancing precision immunotherapy for improved outcomes in these challenging malignancies. Citation Format: Yichen Guo, Rachel Gonzalez, Jina Yom, Bailey Gilmore, Tianli Qu, Xiaomin Hu, Andy (Xi) Han, Zhaoying Guo, Eden Zewdu, Xuan Liu, Wei Fu. Exploring the relationship between PSCA and PD-L1 by a comprehensive tumor immunohistochemical analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6445.

Abstract 4094: Immune modulatory cancer vaccines against IDO1 and PD-L1 trigger distinct pathways and cooperatively reduce tumor growth in preclinical models

Abstract While immune checkpoint inhibitors have shown clinical efficacy in many cancers, drug and immune resistance remain challenging. Indoleamine 2,3-dehydrogenase (IDO1) and Programmed Death Ligand 1 (PD-L1) both contribute to immunosuppression, leading to immune escape and cancer progression. In this context, vaccination to promote T-cell immunity against IDO1+ and PD-L1+ cells is an attractive strategy that demonstrated encouraging clinical results in melanoma (Kjeldsen et al. Nat Med 2021). Our study aims to further evaluate the efficacy and mode of action of combined IDO1 and PD-L1 peptide vaccines. Mice injected with tumor cells and treated with IDO1 or PD-L1 peptides were monitored for tumor growth. Vaccine activity was determined by IFNγ Elispot assay. Gene expression analysis was performed on tumors using Nanostring nCounter PanCancer IO360 Panel. IDO1 and PD-L1 expression were also examined via multiplex immunofluorescence in a human tumor tissue microarray (TMA) panel. Human IDO1 and PD-L1 specific CD4+ T cell clones were isolated and expanded from melanoma patients treated with IDO1/IO102 or PD-L1/IO103 peptide vaccines in combination with aPD1 therapy. Immunofluorescence analysis of murine tumor sections showed expression of IDO1 and PD-L1 by different cell populations. Vaccination against each target led to expansion of specific T cells in splenocytes and reduced tumor growth in MC38 and CT26 models. Combining IDO1 and PD-L1 treatments further enhanced the anti-tumor response. Gene expression analysis of tumors revealed distinct signatures following monotherapy and combination treatments. While PD-L1 vaccination predominantly enhanced the cytotoxic effector T cell function in the tumor microenvironment (TME) and concomitantly increased gene signatures associated with enhanced activation of T effector cells, IDO1 vaccine primarily exerted its effect via reduction in the immune suppression loop. TMA analysis of IDO1+ and PD-L1+ cells in human tumors also revealed that they represent largely distinct cell populations. Lastly, IDO1 and PDL1-specific CD4+ T cell clones from melanoma patients treated with IO102-IO103 vaccine could selectively target cells differentially expressing IDO1 or PDL1. Our data collectively show that cells expressing IDO1 and PD-L1 represent distinct populations in the TME thus targetable by the IDO1-PD-L1 vaccination approach. The vaccines targeting IDO1 and PD-L1 cooperatively reduce tumor outgrowth, and each contributes to the anti-tumor effect through distinct molecular programs regulating immunosuppression in the TME and T cell activation respectively. These data are supported by ex vivo functional assays using target specific T cells from vaccinated patients. Altogether, our data support the use of a dual antigen approach to reduce the immunosuppression and enhance anti-tumor effect. Citation Format: Marion Chapellier, Evelina Martinenaite, Preeyam Patel, Lea Svendsen, Shamaila Munir Ahmad, Hannah Jorinde Glöckner, Marco Carretta, Erika Sutanto-Ward, James DuHadaway, Souvik Dey, Shih-Chun Shen, Dema Ghaban, Marcos Iglesias, Megan Biller, Inés Lecoq, Alexander J. Muller, Mads Hald Andersen, Ayako Wakatsuki Pedersen. Immune modulatory cancer vaccines against IDO1 and PD-L1 trigger distinct pathways and cooperatively reduce tumor growth in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4094.

Abstract 3157: The crosstalk between STAT3 and p53/ERK signaling regulates brain metastasis

Abstract Brain metastasis (BM) affects approximately 10% of cancer patients with metastatic disease, representing a major cause of morbidity and mortality. BM is a complex multi-step process involving various immune checkpoint proteins. Mitogen-activated protein kinase (MAPK), particularly extracellular signal-regulated kinases 1/2 (ERK1/2), and signal transducer and activator of transcription 3 (STAT3) are implicated in tumorigenesis and are critical upstream regulators of Programmed Death Ligand 1 (PD-L1) expression, a common immunotherapy target. Tumor suppressor p53 is shown to regulate STAT3 and ERK1/2 signaling, which are dysregulated in various malignancies. We hypothesize that p53 along with STAT3 and ERK1/2 play a critical role in the initiation and maintenance of BM. Twenty-six BM tumors with various primary sites of origin were used following IRB guidelines. pSTAT3Tyr705, pERK1/2Thr202/Tyr204, mutant p53 (p53mt), and PD-L1 expression was determined by immunohistochemistry. Gene expression analysis of BM was performed on a cDNA microarray. Human brain metastatic breast cancer cells (MDA-MB-231) were treated with STAT3 inhibitor (NSC74859) or MAPK inhibitor (U0126) in regular or astrocytic media to determine cell proliferation and migration by MTT assay and scratch-wound, respectively. ERK1/2 signaling pathway status was determined by Western blotting. Results demonstrated: 1) pSTAT3Tyr705 and pERK1/2Thr202/Tyr204 were expressed profusely at tumor margins, while p53mt was uniformly expressed throughout. 81% of BM expressed p53mt while 86% and 63% expressed pERK1/2Thr202/Tyr204 and pSTAT3Tyr705, respectively. Venn analysis displayed significant overlap between expression, with 62% overlap between p53mt and pERK1/2Thr202/Tyr204 and a 50% overlap between both pSTAT3Tyr705 and pERK1/2Thr202/Tyr204 with p53mt. Expression of PD-L1 was seen in a majority of BM tumors. 2) Gene expression analysis demonstrated alterations in 32 STAT3- and MAPK-associated genes; these included upregulation of stathmin-1 and stathmin-like 3, which control microtubule dynamics in STAT3-related cell migration, and changes in cytokine-related genes, suggesting altered immune responses. 3) Cell proliferation showed augmented growth in astrocytic media (p≤0.05) and was significantly decreased following treatment with NSC74850 or U0126 (p≤0.01). While migration showed a trend towards significance in reduction following NSC74859 (p=0.08), migration stagnated following U0126 treatment in astrocytic media (p≤0.01). 4) pERK1/2Thr202/Tyr204 expression was reduced following U0126 or NSC74859 treatment. These findings suggest activation of STAT3 and ERK1/2 promote BM and suppression of these pathways may lead to a reduction in cell viability and motility. Therefore, this provides compelling evidence for the use of STAT3 and ERK1/2 along with p53 as potential targets for immunotherapy in brain metastatic disease. Citation Format: Sabrina L. Zeller, Eris Spirollari, John V. Wainwright, Simon J. Hanft, Chirag D. Gandhi, Meena Jhanwar-Uniyal. The crosstalk between STAT3 and p53/ERK signaling regulates brain metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3157.

Abstract 6829: Identification of immune suppressive features in tumor-associated endothelial cells (TECs) in EGFR-mutant non-small cell lung cancer via single-cell RNA sequencing

Abstract Introduction: Within the tumor microenvironment (TME), tumor-associated endothelial cells (TECs) exhibit distinct features from normal cells, and diverse phenotypes of TECs result in intratumoral heterogeneity. Here, we aimed to characterize the phenotypes of the TECs of non-small cell lung cancer (NSCLC), identify distinct features that are pivotal in tumor progression, and discover potential therapeutic applications. Methods: We performed single-cell RNA sequencing (scRNA-seq) from 128 NSCLC patients to include I (N=52), II (N=18), III (N=21), and IV (N=14), and compared them with normal cells (N=24). Epidermal growth factor receptor (EGFR)-mutant accounted for 69 samples. EGFR-wild (N=35) was further classified as programmed death-ligand 1 (PD-L1) high (N=14) and low (N=21) with PD-L1 high defined as tumor proportion score &amp;gt; 50%. Results: Twelve distinct EC types were characterized based on clinical information, including EGFR mutations and PD-L1 expression. We classified our subset as normal cells and tumor-enriched ECs, which were further classified as EGFR-wild or mutant ECs. Compared to normal cells, phenotypes such as activated post-capillary veins (APCVs), tip ECs, and endothelial mesenchymal transition (endoMT) ECs were predominantly observed in all tumor-enriched ECs. In EGFR-mutant ECs, ribosomal ECs, and vascular mimicry (VM) ECs were primarily enriched. Trajectory analysis showed that endoMT and VM ECs had lineage tracing of fibroblasts and epithelial cells, respectively. By clinical stage, APCVs, tip ECs, endoMT, and VM ECs were more enriched at advanced stages. PD-L1-high subset had higher expression of adhesion molecules, APCVs, and median transmigration score than other phenotypes. Also, high endothelial venules (HEVs) mediating lymphocyte trafficking to lymphoid organs were enriched in high PD-L1 subset. In the APCVs of EGFR-mutant group, there were interactions related to immune cell suppression and interactions of chemokines/chemokine receptors involved in recruitment. Conclusion: Our findings reveal distinct phenotypes of ECs, including the enrichment of APCVs, tip ECs, and endoMT ECs in all tumor-enriched EC populations, as well as VM ECs in EGFR-mutant ECs. APCVs, which is abundant high PD-L1 subset, play a crucial role in the transmigration progress of immune cells across vascular endothelium. In EGFR-mutant NSCLC, dysfunctional immune cells are recruited into the tumor, along with relatively low transmigration, resulting in poor tumor-killing effect. Citation Format: Su-Jin Choi, Jii Bum Lee, Kyoung-Ho Pyo, Gang-Taik Lee, YoungJoon Park, You Won Lee, Mi Ran Yun, Kyumin Lim, JuHyeon Lee, Min Hee Hong, Sun Min Lim, Byoung Chul Cho. Identification of immune suppressive features in tumor-associated endothelial cells (TECs) in EGFR-mutant non-small cell lung cancer via single-cell RNA sequencing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6829.

Abstract 2519: Alteration of tumor immune microenvironment after recurrence and its impact on the efficacy of anti-PD-1 antibody in resected non-small cell lung cancer patients

Abstract Background: Tumor immune microenvironment (TIME), including programmed death-1 ligand-1 (PD-L1) and CD8-positive tumor-infiltrating lymphocytes (TIL), has been suggested as a potential biomarker to predict the efficacy of anti-PD-1 antibody. Postoperative recurrence in patients with non-small cell lung cancer (NSCLC) is treated with therapeutic strategies similar to those for metastatic disease. However, in postoperative recurrence cases, PD-L1 evaluation is generally based on archival resection specimens, because there is little opportunity for a new biopsy of the recurrent site. Therefore, it remains unclear whether TIME of recurrent lesion is similar to TIME of primary lesion at surgery, and the efficacy of anti-PD-1 antibody for postoperative recurrent NSCLC patients based on TIME status at surgery is unknown. Materials and Methods: Cohort A included 59 patients with advanced and 25 patients with postoperative recurrence NSCLC who treated with first-line pembrolizumab monotherapy. PD-L1 expression and CD8-TIL were evaluated immunohistochemically in tumor specimens obtained at diagnosis in the advanced cases and at surgery in the postoperative recurrence cases. Tumor proportion score for PD-L1 and the extent of CD8-TIL were evaluated and classified as high or low. TIME was categorized into 4 subclasses, according to the respective PD-L1 and CD8-TIL, as follows: (class I) high/high; (class II) low/low; (class III) high/low; and (class IV) low/high. Progression-free survival (PFS) of pembrolizumab was compared based on TIME. Cohort B consisted of 50 NSCLC patients who underwent radical resection, and whose tumor specimens were obtained from recurrent site. As in cohort A, TIME was assessed for paired resection and recurrent tumor samples. Results: In cohort A, the median PFS of pembrolizumab for the advanced cases were 25.7 months in class I (n=25), 2.3 months in class II (n=8), 8.0 months in class III (n=20), and 6.5 months in class IV (n=6) (p&amp;lt;0.001), respectively; while those for the postoperative recurrence cases were 9.0 months (n=7), 4.3 months (n=7), 7.6 months (n=6), and 2.5 months (n=5) (p=0.55), respectively. In cohort B, TIME for resected primary lesion were observed in 9 with class I, 20 with class II, 3 with class III and 18 patients with class IV, respectively. The concordance of PD-L1 category (high vs low) between resected primary lesion and recurrent lesion was 88.0%, while that of TIME classification was 54.0%. Conclusion: TIME classification using tumor specimens just before administration of anti-PD-1 antibody was useful predictive biomarker. However, TIME alterations between resection and postoperative recurrence were observed in many cases, suggesting that TIME based on tumor specimens at surgery may not be useful for predicting the efficacy of anti-PD-1 antibody for postoperative recurrent NSCLC. Citation Format: Yoshiya Matsumoto, Tetsuya Watanabe, Megumi Mizutani, Akira Sugimoto, Hiroaki Nagamine, Yoko Tani, Kenji Sawa, Takuma Tsukioka, Hiroyasu Kaneda, Shigeki Mitsuoka, Noritoshi Nishiyama, Tomoya Kawaguchi. Alteration of tumor immune microenvironment after recurrence and its impact on the efficacy of anti-PD-1 antibody in resected non-small cell lung cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2519.

Abstract 5548: Cannabidiol enhances efficacy of atezolizumab via upregulation of PD-L1 expression by cGAS-STING pathway in triple negative breast cancer cells

Abstract The current treatment for patients with triple negative breast cancer (TNBC) relies on cytotoxic therapy. Currently, atezolizumab and chemotherapy can be combined in patients with TNBC, but this approach is not effective for all patients with low reactivity to atezolizumab. As there is a lack of alternative treatment options, new anti-cancer drugs are urgently needed to enhance atezolizumab reactivity against TNBC. Recent strategies have focused on regulating the expression of programmed death-ligand 1 (PD-L1) or enhancing immune response activation by combining anti-cancer drugs with immune checkpoint inhibitors (ICIs). Cannabidiol (CBD), a cannabinoid component derived from the cannabis plant, has been reported to have anti-cancer therapeutic potential because of its capacity to induce apoptotic cell death in tumor cells while avoiding cytotoxicity in normal cells. Previous studies have demonstrated the effects of CBD on apoptosis in various types of cancer cells. However, the potential role of CBD as an immune modulator in the regulation of PD-L1 expression and the anti-cancer immune response remains to be explored. In this study, we found that CBD stimulated PD-L1 expression in TNBC cells, which significantly induced CBD-mediated cGAS-STING pathway activation. Taken together, we demonstrated that the combination of CBD and anti-PD-L1 antibody enhances the anti-cancer immune response in vitro and in vivo experiments. Our findings identified the mechanism of PD-L1 regulation by CBD in TNBC cells and suggested that CBD could be a potential candidate for the development of new combinatorial strategies with ICIs in TNBC patients. Citation Format: Bu Gyeom Kim, Bo Ram Kim, Dae Yeong Kim, Hyemi Yun, Dayoung Kim, Woo Young Kim, Sanghee Kang, Sun Il Lee, Sang Cheul Oh. Cannabidiol enhances efficacy of atezolizumab via upregulation of PD-L1 expression by cGAS-STING pathway in triple negative breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5548.

Abstract 12: TCR-gated control of costimulatory switch protein (CSP) activation in rTCR-T cells expressing PD1-41BB

Abstract Chimeric antigen receptor (CAR-)/T cell receptor (TCR-)T-based immunotherapies have shown promising results in the treatment of patients suffering from hematological malignancies. However, targeting solid cancer patients with CAR-T/TCR-T cells represents a more challenging approach, due to various factors present within the hostile tumor micro-environment (TME), inhibiting T cell functionality and leading to T cell exhaustion. Programmed cell death ligand-1 (PD-L1) is expressed on tumor cells as well as various cell types within the TME and binds to programmed cell death protein 1 (PD-1) expressed on the surface of activated T cells, thereby inducing T cell exhaustion and mediating tumor immune escape. To impair this inhibitory mechanism and improve TCR-T cell efficacy for the treatment of solid tumors, we use the chimeric costimulatory switch protein (CSP) PD1-41BB that turns the inhibitory signal mediated via the PD-1-PD-L1 axis into a costimulatory one. The CSP-mediated costimulatory signal is TCR-gated, whereby costimulation can only occur if a specific peptide-HLA complex present on a target cell interacts with a recombinant TCR expressed in T cells. In vitro co-cultures of rTCR-T cells expressing the CSP (CSP rTCR-T cells) and antigen-negative or -positive cell lines carrying or lacking PD-L1 demonstrated that CSP rTCR-T cells display functionality only if the respective target antigen is expressed in target cells, but not in the absence of target antigen. PD-L1-positive, antigen-negative tumor cells are not lysed by CSP rTCR-T cells, not even in the presence of antigen-positive tumor cells, showing gated functionality and a favorable safety profile of CSP-armored TCR-T cells. CSP rTCR-T cells displayed enhanced cytokine release and killing after encounter of PD-L1-positive tumor cell lines, compared to tumor cells lacking PD-L1, and showed the capacity to recognize and lyse a large panel of tumor cell lines expressing various levels of HLA-A*02, target antigen and PD-L1 in vitro. 3D spheroids derived from PD-L1-positive, target antigen-positive tumor cell lines mimicking cell-cell interactions within a solid tumor mass efficiently triggered CSP rTCR-T cells, leading to specific IFN-γ release and lysis of tumor spheroids. Furthermore, CSP rTCR-T cells showed enhanced proliferative capacity and expansion in co-cultures with PD-L1-positive tumor cells, compared to tumor cells lacking PD-L1 expression. Importantly, various target antigen-negative healthy cell types expressing or lacking PD-L1 and representing different vital organs were not cross-recognized by CSP rTCR-T cells in vitro. Our preclinical in vitro assessments of CSP rTCR-T cell functionality and safety proved their superior and gated functionality as well as favorable safety profile, showing the great potential for the treatment of cancer patients suffering from advanced solid tumor malignancies. Citation Format: Maja Buerdek, Petra U. Prinz, Kathrin Mutze, Andrea Coluccio, Stefanie Tippmer, Miriam Bosch, Giulia Longinotti, Mario Catarinella, Kathrin Davari, Christiane Geiger, Barbara Loesch, Kirsty Crame, Dolores J. Schendel. TCR-gated control of costimulatory switch protein (CSP) activation in rTCR-T cells expressing PD1-41BB [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 12.

Abstract 3819: Real-world long-term survival outcomes of first-line immunotherapy-based regimens in advanced non-small cell lung cancer

Abstract Background: The real-world survival outcomes of first-line (1L) immunotherapy (IO)-based regimens for the treatment of advanced non-small cell lung cancer (aNSCLC) were assessed utilizing the Flatiron Health database from January 2011 to June 2023. Methods: Adult patients (pts) with aNSCLC receiving 1L IO monotherapy or single-agent IO + chemotherapy on or after January 1, 2016, were identified. Pts were excluded if they had EGFR/ALK mutations or unknown histological type. Overall survival (OS) and real-world progression-free survival (rwPFS) of 1L IO monotherapy and IO + chemotherapy were described using Kaplan-Meier analyses. Results: A total of 14,320 pts were included (5,166 pts receiving IO monotherapy; 9,154 pts receiving IO + chemotherapy). Among pts receiving IO monotherapy, the 1-, 2-, 3-, and 4-year OS rates were 52.3%, 36.5%, 27.4%, and 21.9%, respectively. The corresponding rwPFS rates were 29.2%, 17.5%, 12.7%, and 9.2%. Among pts receiving IO + chemotherapy, the 1-, 2-, 3-, and 4-year OS rates were 50.7%, 32.6%, 23.9%, and 19.2%. The corresponding rwPFS rates were 27.0%, 15.1%, 10.3%, and 7.8%. Table 1 presents the 4-year OS and rwPFS rates stratified by histological type, tumor programmed death ligand 1 (PD-L1) expression level, and Eastern Cooperative Oncology Group (ECOG) performance status. Patients with lower PD-L1 expression level (&amp;lt;1%), worse ECOG performance status (≥2), and squamous cell carcinoma had worse survival outcomes, regardless of the type of 1L treatment received. Conclusions: The real-world survival rates for patients with aNSCLC who were treated with 1L IO-based regimens were lower than those observed in pivotal trials, which indicates an unmet need for the management of newly-diagnosed aNSCLC. However, on average approximately 1 in 11 pts receiving IO monotherapy and 1 in 13 pts receiving IO + chemotherapy remained progression-free at the four year landmark and achieved an extended period of survival. Table: 4-year OS and rwPFS rates 1L IO monotherapy 1L IO + chemotherapy PD-L1 &amp;lt;1% PD-L1 ≥1-49% PD-L1 ≥50% PD-L1 &amp;lt;1% PD-L1 ≥1-49% PD-L1 ≥50% OS by histological type (sample size; 4-year rate, %) Squamous 122; 12.7 329; 14.0 814; 15.1 585; 11.7 647; 15.1 295; 23.3 Non-squamous 231; 16.7 516; 20.0 2563; 26.3 2263; 14.9 2058; 20.8 1313; 28.9 OS by ECOG performance status (sample size; 4-year rate, %) 0-1 193; 17.0 439; 20.8 1880; 27.6 1852; 16.8 1802; 21.9 1065; 28.0 ≥2 89; 6.7 261; 14.5 840; 12.7 478; 5.6 452; 11.1 241; 22.8 rwPFS by histological type (sample size; 4-year rate, %) Squamous 122; 7.6 329; 4.4 814; 6.8 585; 5.2 647; 8.3 295; 9.2 Non-squamous 231; 5.1 516; 10.0 2563; 11.2 2263; 4.3 2058; 6.3 1313; 14.7 rwPFS by ECOG performance status (sample size; 4-year rate, %) 0-1 193; 6.9 439; 10.4 1880; 11.9 1852; 5.4 1802; 6.8 1065; 14.5 ≥2 89; NA 261; 3.7 840; 5.0 478; 2.2 452; 3.9 241; 8.2 Citation Format: David Waterhouse, Saurabh Ray, Keith A. Betts, Sophie Gao, Yong Yuan, Manasvi Sundar, Shumin Rui, David Stenehjem. Real-world long-term survival outcomes of first-line immunotherapy-based regimens in advanced non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3819.

GABA/baclofen stabilizes PD-L1 and enhances immunotherapy of breast cancer

The programmed death-ligand 1 (PD-L1) on the surface of tumor cells binds to the receptor programmed cell death protein 1 (PD-1) on effector T cells, thereby inhibiting the anti-tumor immune response. Immune checkpoint blockade (ICB) therapy targeting PD-1/PD-L1 has been approved for the treatment of human cancers with lasting clinical benefit. However, many cancer patients did not respond to anti-PD-1/PD-L1 antibody blocking therapy or drugs targeting PD-1/PD-L1. Recent studies have shown that the response to PD-1/PD-L1 blockade may be related to the PD-L1 abundance of tumor cells. Therefore, it is of crucial significance to find drugs to regulate the expression of PD-L1, which can provide new strategies to improve the response rate and efficacy of PD-1/PD-L1 blocking in cancer treatment. Here, we found that GABA and baclofen, upregulates the protein level of PD-L1 by reducing the mRNA and protein levels of STUB1, a E3 ubiquitin ligase, thereby decreasing the interaction between STUB1 and PD-L1, and ultimately stabilizing PD-L1. Notably, GABA and baclofen did not affect cell proliferation in vitro, while in the treatment of breast cancer in mice, the therapeutic effect of baclofen combined with anti-PD-L1 antibody is significantly better than that of using anti-PD-L1 antibody alone by stimulating tumor infiltration of CD8+ T cells and antitumor immunity. Taken together, we unveiled a previously unappreciated role of GABA/baclofen in stabilizing PD-L1 and enhancing the immunotherapy of breast cancer.

A new strategy for immunotherapy of microsatellite-stable (MSS)-type advanced colorectal cancer: Multi-pathway combination therapy with PD-1/PD-L1 inhibitors.

Colorectal cancer (CRC) is a frequent gastrointestinal malignancy with high rates of morbidity and mortality; 85% of these tumours are proficient mismatch repair (pMMR)-microsatellite instability-low (MSI-L)/microsatellite stable (MSS) CRC known as 'cold' tumours that are resistant to immunosuppressive drugs. Monotherapy with programmed death 1 (PD-1)/programmed death ligand 1 (PD-L1) inhibitors is ineffective for treating MSS CRC, making immunotherapy for MSS CRC a bottleneck. Recent studies have found that the multi-pathway regimens combined with PD-1/PD-L1 inhibitors can enhance the efficacy of anti-PD-1/PD-L1 in MSS CRC by increasing the number of CD8+ T cells, upregulating PD-L1 expression and improving the tumour microenvironment. This paper reviews the research progress of PD-1/PD-L1 inhibitors in combination with cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) inhibitors, oncolytic virus, intestinal flora, antiangiogenic agents, chemotherapy, radiotherapy and epigenetic drugs for the treatment of pMMR-MSI-L/MSS CRC.